Non-penetrative sex (oral sex may
or may not be penetrative) and mutual masturbation have been
referred to as "outercourse".[3][4][5][6]
"Outercourse" is something of a misnomer, as it contrasts "outer"
with "inter" but the "inter" in "intercourse" means "between two
people" or beings. It does not describe being inside or outside of
the body. The word sex, in the context of sexual
intimacy, is often, if not universally, understood to include any
mutual genital stimulation, i.e. both intercourse
and outercourse.[7]

Mating is the term most
often used to refer to sexual intercourse between animals other
than humans; for most, mating occurs at the point of estrus (the most
fertile period of time in the female's reproductive cycle),[8][9]
which increases the chances of successful impregnation.
However, bonobos,[10]dolphins,[11]
and chimpanzees are
known to engage in sexual intercourse even when the female is not
in estrus, and to engage in sex acts with same-sex partners.[12]
In most instances, humans have sex primarily for pleasure.[13]
This behavior in the above mentioned animals is also presumed to be
for pleasure,[14]
which in turn strengthens social bonds.

Modern Judaism, Christianity, and Islam view sexual intercouse
between husband and wife as a spiritual and edifying action, while
extra-marital sex is viewed as immoral. The limits of marriage and concubinage within
these traditions has changed over time, along with corresponding
views of acceptable sexual behavior. The teachings of Hinduism and Buddhism on sexuality have
differing interpretations, though mostly they are associated with
marriage. Buddhism's injunction to "refrain from sexual misconduct"
finds its interpretation and practical definitions within the
particular Buddhist communities. However, within each of these
major religious traditions exists subgroups with varying stances on
acceptable sexual practices, and some religious groups prohibit
their members from engaging in sexual intercourse altogether.

However, some terrestrialarthropods do use external fertilization. For
primitive insects, the male
deposits spermatozoa on the substrate, sometimes
stored within a special structure, and courtship involves inducing the female to
take up the sperm package into her genital opening; there is no
actual copulation. In groups such as dragonflies and spiders, males extrude sperm into
secondary copulatory structures removed from their genital opening,
which are then used to inseminate the female (in dragonflies, it is
a set of modified sternites on the second abdominal segment;
in spiders, it is the male pedipalps). In advanced groups of insects, the
male uses its aedeagus, a
structure formed from the terminal segments of the abdomen, to
deposit sperm directly (though sometimes in a capsule called a "spermatophore")
into the female's reproductive tract.

In humans

Vaginal sexual intercourse, also called
coitus, is the human form of copulation. While its
natural purpose and result is reproduction, it is often performed
entirely for pleasure and/or as an expression of love and emotional
intimacy.[2][13]
Sexual intercourse typically plays a powerful bonding role; in
many societies it is normal for couples to have frequent
intercourse while using birth control, sharing pleasure and
strengthening their emotional bond through sex even though they are
deliberately avoiding pregnancy.[13]

Sexual intercourse may also be defined as referring to other
forms of insertive sexual behavior, such as oral sex and anal intercourse. The phrase
to have sex can mean any or all of these
behaviors, as well as other non-penetrative sex acts not considered
here. Sex
positions often play a part in all human sexual
interactions.

Coitus may be preceded by foreplay, which leads to sexual arousal of
the partners, resulting in the erection of the penis and natural lubrication of the vagina. To engage in coitus, the
erect penis is inserted into the vagina and one or both of the
partners move their hips to move the penis backward and forward
inside the vagina to cause friction, typically without fully removing the
penis. In this way, they stimulate themselves and each other, often
continuing until orgasm in
either or both partners is achieved. Penetration by the hardened
erect penis is also known as intromission, or by
the Latin name immissiopenis (Latin for
"insertion of the penis").

Coitus is the basic reproductive method of humans. During
ejaculation, which usually accompanies male orgasm, a series of
muscular contractions delivers semen containing male gametes known
as sperm cells or spermatozoa from the penis into the vagina.

The subsequent route of the sperm from the vault of the vagina
is through the cervix and into
the uterus, and then into the
fallopian
tubes. Millions of sperm are present in each ejaculation, to
increase the chances of one fertilizing an egg or ovum. When a fertile ovum from the female is
present in the fallopian tubes, the male gamete joins with the
ovum, resulting in fertilization and the formation of a new
embryo. When a fertilized ovum
reaches the uterus, it becomes implanted in the lining of the
uterus, known as endometrium, and a pregnancy begins.

Unlike most species, human sexual activity is not linked to
periods of estrus and can take place at any time during the
reproductive cycle, even during pregnancy.[15]

Coitus
difficulties

Anorgasmia is
regular difficulty reaching orgasm after ample sexual stimulation,
causing personal distress. This is much more common in women than
men. The physical structure of the act of coitus favors penile
stimulation over clitoral stimulation. The location of the clitoris
then often necessitates manual stimulation in order for the female
to achieve orgasm. About 15 percent of women report difficulties
with orgasm, and as many as 10 percent of women in the United
States have never climaxed. Even women who orgasm on a regular
basis only climax about 50 to 70 percent of the time.[16]

Some males suffer from erectile dysfunction (ED), or impotence, at least occasionally. For those
whose impotence is caused by medical conditions, prescription drugs
such as Viagra, Cialis, and Levitra are available.
However, doctors caution against the unnecessary use of these drugs
because they are accompanied by serious risks such as increased
chance of heart attack. Moreover, using a drug to counteract the
symptom—impotence—can mask the underlying problem causing the
impotence and does not resolve it. A serious medical condition
might be aggravated if left untreated.

The American Urological Association (AUA) estimates that
premature ejaculation could affect 27 to 34 percent of men in the
United States. The AUA also estimates that 10 to 12 percent of men
in the United States are affected by erectile dysfunction. Vaginismus is involuntary
tensing of the pelvic floor musculature, making coitus distressing,
painful, and sometimes impossible.[19][20]Dyspareunia is a
medical term signifying painful or uncomfortable intercourse, but
does not specify the cause.[21][22]

Although disability-related pain and mobility
impairment can hamper intercourse, in many cases the most
significant impediments to intercourse for individuals with a
disability are psychological.[23]
In particular, people who have a disability can find intercourse
daunting due to issues involving their self-concept as a sexual being,[24][25]
or partner's discomfort or perceived discomfort.[23]

Functions of sex beyond
reproduction

Health
benefits

Sex between cohabiting partners lowers blood pressure and reduces stress,
according to Stuart Brody, professor of psychology at the
University of the West of Scotland. Brody's team monitored 24 women
and 22 men who were exposed to stressful situations, such as
speaking in public and doing verbal arithmetic, and kept records of
their sexual activity. The men and women who had penile-vaginal
intercourse responded more positively to stress "than those who
engaged in other sexual behaviors or abstained".[27][28] A
study by Keith Light of the University of North Carolina went as
far as to find a link between "partner hug" and lower blood
pressure in women.[27][29]

Frequent sexual intercourse was held to reduce the risk of the
common cold by Carl Charnetski and Francis X. Brennan of Wilkes
University in Wilkes-Barre, Pa. These scientists linked
frequent sexual intercourse (once or twice a week) to increased
production of the antibody
called Immunoglobulin A or IgA, which can
protect the body from getting colds and other infections. They took
samples of saliva, which
contain IgA, from 112 college students who reported the frequency
of sex they had. The students in the "frequent" group had higher
levels of IgA than those in the other three groups, consisting of
people who were celibate,
had sex less than once a week, or had it "very often" (three or
more times weekly). The other three groups had comparable IgA
levels.[27][30]
Charnetski and Brennan had previously shown that exposure to
elevator music has a similar effect on IgA levels.[31]

"Sex is a great mode of exercise," according to Patti Britton,
PhD, past
president of the American Association of Sexuality Educators,
Counselors and Therapists (AASECT) and currently host of the
website "Your Sex Coach". She notes that thirty minutes of sex
burns 85 calories or more. She concludes that 42 half-hour
sessions, or 21 hour-long sessions, will burn 3,570 calories -
sufficient to lose one pound.[27]

"Boosting self-esteem" was one of 237 reasons people have sex,
collected by University of
Texas researchers and published in the journal Archives of
Sexual Behavior. Some subjects who already had high
self-esteem said they sometimes have sex to "feel even better".[27]

Sexual intimacy, as well as orgasms, increases levels of the
hormone oxytocin, also
known as "the love hormone" which helps people bond and build
trust. Researchers from the University of Pittsburgh and
the University of
North Carolina at Chapel Hill evaluated 59 premenopausal women
before and after warm contact with their husbands and partners
ending with hugs. They found that the more contact, the higher the
oxytocin levels. Oxytocin allows people to feel the urge to nurture
and to bond. Generosity has also been credited and linked
to a higher level of oxytocin. In addition, as the hormone oxytocin
surges, endorphins increase, and pain declines. In a study
published in the Bulletin of Experimental Biology and
Medicine, 48 volunteers who inhaled oxytocin vapor and then
had their fingers pricked lowered their pain threshold by more than
half. The oxytocin released during orgasm also promotes sleep.[27]

Men who have frequent ejaculations, especially men in their 20s,
may reduce their risks of prostate cancer later in life. Australian researchers
reported in the British Journal of Urology International
that they followed men diagnosed with prostate cancer and those
without. They found no association of prostate cancer with the
number of sexual partners as the men reached their 30s, 40s, and
50s, but men who had five or more ejaculations weekly while in
their 20s reduced their risk of getting prostate cancer later by a
third. Another study, reported in the Journal of the
American Medical Association, "found that frequent
ejaculations, 21 or more a month, were linked to lower prostate
cancer risk in older men, as well, compared with less frequent
ejaculations of four to seven monthly".[27]

During sex, pelvic floor muscle exercises known as Kegels offer
benefits for women. More sexual pleasure is expected to result,
strengthening of the area, and help to minimize the risk of
incontinence later in life.[27]

Social and other
behaviors

Humans,
bonobos,[10]
chimpanzees and dolphins[11]
are species known to engage in heterosexual behaviors even when the
female is not in estrus, which is a point in her reproductive cycle
suitable for successful impregnation. These species, and others,
are also known to engage in homosexual behaviors.[12]

In both humans and bonobos, the female undergoes relatively concealed
ovulation so that both male and female partners commonly do not
know whether she is fertile at any given moment. One possible
reason for this distinct biological feature may be formation of
strong emotional bonds between sexual partners important for social
interactions and, in the case of humans, long-term partnership
rather than immediate sexual reproduction.[13]

Humans, bonobos and dolphins are all intelligent social animals,
whose cooperative behavior proves far more successful than that of
any individual alone. In these animals, the use of sex has evolved
beyond reproduction apparently to serve additional social
functions. Sex reinforces intimate social bonds between individuals
to form larger social structures. The resulting cooperation
encourages collective tasks that promote the survival of each
member of the group.

Alex Comfort
and others posit three potential advantages of intercourse in
humans, which are not mutually exclusive: reproductive, relational,
and recreational.[13][32] While
the development of the Pill and other highly effective forms
of contraception in the mid- and late 20th
century increased people's ability to segregate these three
functions, they still overlap a great deal and in complex patterns.
For example: A fertile couple may have intercourse while
contracepting not only to experience sexual pleasure
(recreational), but also as a means of emotional intimacy
(relational), thus deepening their bonding, making their
relationship more stable and more capable of sustaining children in
the future (deferred reproductive). This same couple may emphasize
different aspects of intercourse on different occasions, being
playful during one episode of intercourse (recreational),
experiencing deep emotional connection on another occasion
(relational), and later, after discontinuing contraception, seeking
to achieve pregnancy (reproductive, or more likely reproductive and
relational).

Sexual acts, other than as a means of reproduction, are varied:
Oral sex consists of all the sexual activities that involve
the use of the mouth, tongue, and possibly throat to stimulate genitalia. It is sometimes
performed to the exclusion of all other forms of sexual activity.
Oral sex may include the ingestion or absorption of semen or vaginal
fluids. Other non-penetrative sex acts are also common. While
there are many sexual acts involving the anus, anal cavity, sphincter valve and/or rectum, the most common meaning
of anal sex is the
insertion of a man's penis into another person's rectum.

Sexual ethics and
legality

Unlike some other sexual activities, vaginal intercourse has
rarely been made taboo on religious grounds or by
government authorities, as procreation is inherently essential to
the continuation to the species or of any particular genetic line,
which is considered to be a positive factor, and indeed, enables
most societies to continue in the first place. Many of the cultures
that had prohibited sexual intercourse entirely no longer exist; an
exception is the Shakers, a
group that reached a size of about 6,000 full members in 1840, but
as of 2009 had only three
members left.[34] There
are, however, many communities within cultures whose members
refrain from any form of sex, especially members of religious
orders and the priesthood in the Roman Catholic
Church and Mahayana Buddhist
monks. Within some ideologies, coitus has been considered the
only "acceptable" sexual activity. Relatively strict designations
of "appropriate" and "inappropriate" sexual behavior have been
defined by human cultures for thousands of years. These legal or
cultural restrictions may include:

Most countries have age of consent laws specifying the
minimum legal age for engaging in sexual intercourse. Sexual
intercourse with a person against their will, or without their informed legal
consent, is referred to as rape, and is considered a serious crime in most
countries. Some countries codify as rape any sex with mentally
handicapped persons of any age. Sex, regardless of consent, with a
person under the age of consent is often considered to be sexual assault or
statutory
rape. The age of consent varies from country to country and
often by state or region; commonly, the age of consent is set
anywhere between twelve and eighteen years of age, with sixteen
years being the most common age the law sets. Sometimes, the age of
consent is lowered for people near the same age wishing to
participate in intercourse. For example, in Canada, the minimum age of consent for all
couples is 16. However, the age of consent can go below 16 on the
condition that the couple still are not two years of age apart.
Religions may also set differing ages for consent, with Islam
setting the age at puberty, which can vary from around 10 to 14.
There are often further restrictions on age concerning anal sex,
homosexual sex, or sex with someone in a position of trust or
authority, such as a teacher or caretaker.

Though there are exceptions, most non-Islamic and multi-cultural
countries no longer criminalize consensual sex of any sort among
adults. In contrast, Islamic countries typically
imprison or execute homosexuals. Iran alone is estimated to have executed 4,000
persons for homosexual sex since the Islamic
Revolution of 1979, including two teenage boys in 2005.[36]

Religious and philosophical
views

Modern humans, who date from approximately 400,000 years ago,
have always reproduced by sexual intercourse. Modern religions and
philosophies, on the other hand, are all less than 10,000 years
old, and it is impossible to determine if there were earlier
religious or philosophical views on sexual intercourse. Some
religious traditions, such as Christianity, hold that the first
humans came into being by an act of God and not through human
sexual intercourse. That is, after each pair of animals or humans
were created, they began reproducing through sexual intercourse.
Others, such as Mormonism, hold that there is a Heavenly Father and
Mother whose actions resulted in earthly children.

Religious and philosophical viewpoints on sexual intercourse are
varied. Some hold that person should engage in whatever sexual act
they desire so long as it does not involve children, animals, or
those who cannot or will not willingly consent to participate.
Others hold that sexual intercourse is acceptable even with an
unwilling partner, so long as the two are married (also known as
"conjugal rights" or "marital rights").

Ancient Judaism and early Christianity, allowed sexual relations
between one male and more than one female (polygamy), and Islam still does. The Bible required that a brother have
sexual intercourse with his brother's widowed, childless spouse so
as to provide her children and forbade coitus interruptus in such
cases. Modern Judaism views sex and reproduction as the holiest of
human acts, the act through which one can imitate God, the
Creator.

The medieval Christian Church condemned coitus outside marriage
and placed strict limits on permissible practices within it.
Penance of bread, water, and abstinence was imposed for exotic
congress, the following being one example:

Dorsal sex (woman on top): three years penance

Lateral, seated, standing: 40 days

Coitus retro (rear entry): 40 days

Mutual masturbation: 30 days

Inter-femural (ejaculation between the legs): 40 days

Coitus in terga (anal sex): three years if committed
with an adult; two years if with a boy; seven years for habitual
offenders; and 10 years if with a cleric[37]

Today there is wide variation of opinion and teaching about
sexual intercourse within and between the three Abrahamic religions, with some communities
limiting sexual activity strictly to intercourse and others making
practically no pronouncements on sex at all. Islam views sex within
marriage as something pleasurable, even a spiritual activity and a
duty. Some Moslems hold that male martyrs for the Islamic faith
will receive multiple virgin females as a reward in the afterlife.
Christianity views sex in marriage as holy. It affirms that
everything God created, including sex, is good.

The Kama Sutra is a
well-known product of Hindu society that extols the benefits of
sexual intercourse.

Pope John Paul II saw the human body as the only
one capable of making the invisible — the spiritual and the divine
— visible.[38] He
taught that human beings were created to freely choose to give
themselves, expressing this through the language of their bodies.
For him, marital sexual love is a symbol of their total mutual
self-donation, and further fosters it, and thus it has great
beauty, is a form of worship and an experience of the sacred. Non marital sex
(masturbation and fornication) and contraception falsify the
language of the body, he says, because they use the body for
selfish ends and treats embodied persons as things and objects.[39][40]

Hinduism has varied views about sexuality, but Hindu society, in
general, perceives both pre-marital and extramarital sex to be
immoral and shameful, notwithstanding popular culture. The Kama Sutra is a
well-known product of Hindu society that extols the benefits of
sexual intercourse. Buddhist ethics, in its most common
formulation, holds that one should neither be attached to nor crave
sensual pleasure. Some Asian societies shaped by Buddhist
traditions take a strong ethical stand on sexual behavior. In the
Bahá'í faith, sexual relationships are
permitted only between a husband and wife.

Unitarian Universalists and Neopagans, with an emphasis on strong
interpersonal ethics, do not place boundaries on the occurrence of
sexual intercourse among consenting adults other than the vows that
individuals may have taken voluntarily.

Objectivism, the
philosophy espoused by Ayn
Rand, like other similar movements including libertarianism
holds that people should pursue the lifestyle that makes them
happiest so long as others are not hurt.

^ "Females of
almost all species except man will mate only during their fertile
period, which is known as estrus, or heat..." Helena Curtis (1975). Biology. Worth
Publishers. pp. 1065. ISBN
0879010401.

^ ab
Dinitia Smith, "Central Park Zoo's gay penguins ignite debate",
San Francisco Chronicle (February 7, 2004). Article is
mainly about gay penguins but also mentions homosexuality in
dolphins, and also says 'In bonobos, she noted: "you see
expressions of sex outside the period when females are fertile."'
Available online at http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/02/07/MNG3N4RAV41.DTL.